The goal of this project is to gain a better understanding of the cellular immune events and possible immunopathogenesis of sarcoid granuloma. Employing a membrane market, a population of "activated" T cells in increased numbers has been identified in the peripheral blood of patients with acute sarcoidosis. Since animal studies suggest that stimulated cells "home" to sites of inflammation and also have important immunoregulatory roles in lymphocyte and mononuclear phagocytic function, the specific goal of this project will be to define the role of "activated" T cells in human granulomatous disease (i.e., sarcoidosis). This will be accomplished by (1) a prospective longitudinal study to correlate disease activity with "activated" T cells in untreated and steroid-treated sarcoidosis, (2) in vitro studies of enriched populations of in vivo (sarcoid) and in vitro (Con A) "activated" T cells to define their function (mitogenic response, chemotaxis, suppression of B and T cell proliferation and stimulation of mononuclear phagocytes) and (3) in vitro studies of normal and sarcoid mononuclear phagocytes not only to test factors in sarcoidosis that stimulate mononuclear phagocytes to form giant cells but also to determine how the stimulated cells function (stimulation of lymphocytes to produce "activated" T cells, stimulation of other mononuclear phagocytes). Sarcoidosis presents a unique opportunity to study the interrelationship of lymphocytes and macrophages in a human granulomatous disease of unknown etiology.